1. Field of the Invention
This invention relates to a water-tube boiler and, in particular, a multitubular or shell-and-tube type once-through boiler in which a pair of upper and lower headers are connected by means of a plurality of vertical water-tubes communicating therewith. The once-through boiler according to this invention has a simple structure, exhibits excellent heat transfer efficiency, and requires only a relatively small installation area.
2. Description of the Prior Art
A variety of multitubular once-through boilers have been described in past patent and other technical literatures. Most of these well-known once-through boilers comprise a burner, a pair of ring-shaped upper and lower headers, and a plurality of vertical water-tubes connecting the upper and lower headers, the water-tubes being in contact with each other to form a ring-shaped water-tube wall. However, multitubular once-through boilers of this type have drawbacks such as insufficient heat transfer area per unit volume and a remarkably large installation area, since their water-tubes are blank pipes.
To overcome the above drawbacks, many attempts have been made to improve the water-tubes in the boilers. One approach has been to dispose the water-tubes a slight distance from each other and to fix to each a longitudinal fin extending along approximately the whole length thereof (see Japanese Examined Utility Model Publication No. 56-54401, published on Dec. 18, 1981, which corresponds to Japanese Utility Model Application No. 47-119115 filed on Oct. 13, 1972 in the name of Miura Co., Ltd.). Another approach, one of the present inventor, has been to dispose the water-tubes a slight distance from each other and to dispose at the area next to each two adjacent water-tubes, on the side of the tubes facing the outer wall or shell of the boiler, a barrier plate having an approximately V-shaped cross-section corresponding to the configuration of said area, the barrier plate being disposed to provide a small clearance with the surface of the water-tubes (see Japanese Examined Utility Model Publication No. 53-43921, published on Oct. 21, 1978, which corresponds to Japanese Utility Model Application No. 51-43496 filed on Apr. 7, 1976 in the name of Miura Co., Ltd.). These approaches effectively increase the heat transfer efficiency of the boiler, but cannot fully and sufficiently solve the problems set forth above.